fix(webapp): treat FAILED buffered runs as terminal in spans/trace routes + align workerQueue default

Addresses three Devin review findings on PR #3755:

- api.v1.runs.\$runId.spans.\$spanId.ts and api.v1.runs.\$runId.trace.ts:
  the buffered-run response branch hardcoded isError:false and only
  checked CANCELED for isPartial, so a FAILED buffered run rendered as
  "still in progress" — SDK consumers would poll forever. Now derives
  both flags from CANCELED and FAILED, matching syntheticTrace.server.ts.
- ApiRetrieveRunPresenter.synthesiseFoundRunFromBuffer: workerQueue
  defaulted to "main" while syntheticSpanRun.server.ts uses "". The API
  response's `region` is sourced via `run.workerQueue || undefined`, so
  "main" was advertising a region the run hadn't yet been assigned to.
  Aligned to "" so unassigned buffered runs coerce to region: undefined.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: d-cs

apps/webapp/app/presenters/v3/ApiRetrieveRunPresenter.server.ts

@@ -647,7 +647,11 @@ function synthesiseFoundRunFromBuffer(buffered: SyntheticRun): FoundRun {
     attemptNumber: null,
     engine: "V2",
     taskEventStore: "taskEvent",
-    workerQueue: buffered.workerQueue ?? "main",
+    // Empty string when absent (matches syntheticSpanRun.server.ts and lets
+    // `createCommonRunStructure`'s `run.workerQueue || undefined` coerce the
+    // API response's `region` to undefined instead of advertising a
+    // misleading "main" region for a not-yet-assigned buffered run).
+    workerQueue: buffered.workerQueue ?? "",
     parentTaskRun: null,
     rootTaskRun: null,
     childRuns: [],

apps/webapp/app/routes/api.v1.runs.$runId.spans.$spanId.ts

@@ -89,15 +89,20 @@ export const loader = createLoaderApiRoute(
       if (resolved.run.spanId !== params.spanId) {
         return json({ error: "Span not found" }, { status: 404 });
       }
+      // CANCELED and FAILED are terminal states. A FAILED buffered run is
+      // errored (drainer exhausted retries or gate rejected it) and must
+      // not signal "still in progress" — mirrors syntheticTrace.server.ts.
+      const isCancelled = resolved.run.status === "CANCELED";
+      const isFailed = resolved.run.status === "FAILED";
       return json(
         {
           spanId: resolved.run.spanId,
           parentId: resolved.run.parentSpanId ?? null,
           runId: resolved.run.friendlyId,
           message: resolved.run.taskIdentifier ?? "",
-          isError: false,
-          isPartial: resolved.run.status !== "CANCELED",
-          isCancelled: resolved.run.status === "CANCELED",
+          isError: isFailed,
+          isPartial: !isCancelled && !isFailed,
+          isCancelled,
           level: "TRACE",
           startTime: resolved.run.createdAt,
           durationMs: 0,

apps/webapp/app/routes/api.v1.runs.$runId.trace.ts

@@ -97,12 +97,13 @@ export const loader = createLoaderApiRoute(
                 events: [],
                 startTime: buffered.createdAt,
                 duration: 0,
-                isError: false,
-                // Cancelled is a terminal state — the span shouldn't
-                // signal "still in progress" once it's been cancelled.
-                // Mirrors the sibling api.v1.runs.$runId.spans.$spanId.ts
-                // and syntheticTrace.server.ts logic.
-                isPartial: buffered.status !== "CANCELED",
+                isError: buffered.status === "FAILED",
+                // CANCELED and FAILED are terminal states — the span
+                // shouldn't signal "still in progress" once the run has
+                // reached either. Mirrors the sibling
+                // api.v1.runs.$runId.spans.$spanId.ts and
+                // syntheticTrace.server.ts logic.
+                isPartial: buffered.status !== "CANCELED" && buffered.status !== "FAILED",
                 isCancelled: buffered.status === "CANCELED",
                 level: "TRACE",
                 queueName: buffered.queue ?? undefined,